Measuring and conteol apparatus



June 24, 1941. E, c, WIEGMANN 2,247,267

MEASURING AND CONTROL APPARATUS Filed Dec. 9. 1937 :4 so 94 INVENTOR. aowm QWIEGMANN .AITDRNEY Patented June 24, 1941 Ed 0. Wiegmann,

elphia, Pa, assignorto The Brown trument Company, Thiel- =l Pa, a coration of Pennsylvania.

Application December 9, 1937, Serial No. i'itdldl it on. (cl.- ass-s2 The present invention relates to measuring and control instruments of the type that are used to measure a variable such as pressure or temperature and to control the condition being measured so that it may be kept at some predetermined value. In general the device disclosed herein pertains to a self contained instrument in which a novel pneumatic relay is used to vary the setting of a so-called proportioning system that in turn controls the positioning of a valve which varies the value of the condition being measured.

More specifically my invention includes a pair of bellows that are alternately expanded and compressed to act as a compressor to supply air which actuates a relay in accordance with the value of the condition relative to a desired value thereof. This relay in turn moves a contact along a resistance of a balanced electrical circuit of the proportioning system to unbalance the same.

This unbalance is in turn used to energize a motor which regulates a valve controlling the condition and rebalances the circuit.

The various ieatures'bf novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawing:

Fig. 1 is a view including an elevation of a control instrument with parts broken away and including a diagrammatic representation of furnace control provisions external to the instrument and cooperating with the instrument to maintain predetermined temperature conditions.

Fig. 2 is a perspective view showing the arrangement of the flappers and nozzles.

Fig. 3 is a perspective view showing a portion of the apparatus shown in Fig. 1.

In the invention my improved control instrument comprises mechanism located in an instrument casing I, which may be of any conventional instrument casing size and form, and includes a front door 2, with a hinge connection 3 between the door and casing body, said instrument being employed to adjust the fluid fuel supply valve 4 of a furnace or heater 5, as required to maintain a predetermined furnace temperature to which the device 6 is responsive. As shown, the device 6 is the bulb of a fluid pressure thermometer, the pressure of which is transmitted by a tube l to the stationary end of a Bourdon tube helht forming part of the instrument mechanism. The free end of the helix t gives angular movements about a shaft a, coaxial with the helix, to a crank arm it as the thermometer temperature increases or decreases. The angular movements of arm in shift link H and oscillate bell-crank it about shaft i3 to which it is attached, to thereby oscillate a pen arm id whose upper end is formed as a yoke, the other leg of which is also attached to shaft 53. Oscillation of bell crank iii about its axis also oscillates lever it about its support ill by means of link ill, and thereby gives longitudinal movement to a flapper valve adjusting link it. The latter connects lever it to a float ing lever ill, which is pivotally connected at it to a supporting lever 2 l the latter being plvotally supported at 22 and biased in a counter-clockwise direction by spring 22a. 7

The lever it thru a pin projection it engages the dapper valves is and it pivoted at it and each having a gravitational bias clockwise and counter clockwise respectively to engage and close the discharge thru vents or bleeder outlet nozzles 21 and 28. The nozzle El is supplied with 'air from the driving bellows 29 by means of ducts 3d and 3! the former of which also leads to balancing bellows 32. In like manner nozzletd is supplied with air from driving bellows 33 by means of ducts 34 and. 35, the former of which leads to a second opposed balancing bellows 36.

The pair of driving bellows are connected at their opposed ends by a rod 31 having a pin 38 extending therefrom and received by a slot in lever 39 pivoted in the casing at 40. The lever 39 has another slot 4| therein which receives an eccentric pin 42 on a disc 43. The bellows 29 and 33 are alternately compressed and expanded by rotation of the disc 43 mounted on a shaft 44 driven thru suitable gearing 45 from a motor 46. This same motor 46 is used to drive chart 41, mounted on a hub (not shown) in the casing, at a suitable rate of, for example, once every twenty-four hours.

The alternate expansion and contraction of the balancing bellows 32 and 36, when this is permitted in a manner to be later described, is used to move a contact member 48 over a. resistance 49. This is accomplished by mounting contact 48 on one arm of a bell crank 50 which is pivoted at 5|, the other arm of the bell crank having an oil-set extension with rack teeth 52 formed thereon. The bellows 32 has a rod 53 attached to its end for movement therewith and pivoted to the outer end of the rod 53 is a pawl 54 for engaging with teeth 52. In a like manner bellows 36 has a rod 55 attached to its end, to the other end of which is pivoted a pawl 56 for engaging other of the teeth 52. A throttling range selector is provided for adjusting the amount of follow-up movement given to lever 2| by a given angular movement of bell crank 50 and consists of a calibrated dial 51 to which is attached a lever 58,

the two being mounted for pivotal movement in the casing. Pivotally attached to the outer end of lever 58 is another lever 59 which has a pin 60 in its outer end. This pin extends between lever 21 and bell crank 56 and its position of contact between the two levers may be changed by rotating dial 51.

In the operation of the relay the lever 2|. is normally positioned, when the temperature is at the desired value, so that the lever 19 is horizontal and pin 23 prevents either flapper 24 or 25 from contacting the nozzles 21 or 28, therefore both nozzles are open. As the motor 46 rotates to reciprocate rod 31 the driving bellows 29 and 33'are alternately compressed and since the nozzles are unobstructed air can be exhausted thru them and there is no movement of the balancing bellows 32 or 36. If, however, the temperature to which bulb 5 is subjected increases, helix 8 will be expanded to move link 11 to the left and bellcrank l2 clockwise. Such a movement will cause lever 15 to be lifted and in turn move link 18 upward and lever 19 with pin 23 clockwise around pivot 2|]. 7 This permits flapper 24 to move toward nozzle 21 under its gravity bias and close the nozzle so that when bellows 29 is next contracted air cannot escape therethru. As a consequence balancing bellows 32 is expanded forcing rod 53 and pawl 54 to the left to move bell crank 50 clockwise and shift contact 48 downwardly along resistance 48. This motion is transmitted to lever 2|, the lower end of which is moved to the right by spring 220. thus moving lever 18 and pin 23 to the right to open nozzle 21 and again restore the system to equilibrium. In a like manner if there is a decrease in the temperature of bulb 6 the balancing bellows 36 is expanded to move contact 48 upward along resistance 49 and force levers 2! and 19 to the left to restore equilibrium to the system.

Angular adjustments of the bell crank 58, in a manner above described, move contact 48 along resistance 48 to control the adjustment of the heater supply valve 4 and gives the latter adjustment movements proportional to the adjustment movements of the bellcrank 56 and contact 48. The proportioning means comprise a portion forming a part of .the control instrument and located with the instrument casing i, and a larger portion external to the casing l and connected to the instrument portion only by electrical conductors extending through the instrument casing wall. The portion of the proportioning means within the instrument casing comprises an electrical resistance 49, ordinarily, and as shown, wound into a helical coil on a supporting body of insulating material, and so disposed that as the contact 48 moves through its range of oscillation, it will engage the resistance conductor 49 at successively different points along its length, the particular point engaged at any time being dependent on the angular position of bell-crank 56 and contact 48 at the time. Conductors 6| and 62 are connected to the ends of the resistance conductor 48 and a conductor 63 is connected to the switch'or contact 48. The conductors 61, 62, and 63, are conveniently included in a single cable extending through a part 64 mounted in an opening in the instrument casing body, such as is points along the length of the latter as the angular position of the shaft 66 is adjusted. The resistances 48 and 65, conductors 6|, 62, and 63, and contacts 48 and 61, form parts of a Wheatstone bridge arrangement which is energized by a transformer 68, the terminals of the secondary winding of that transformer being connected by conductors 88 and 18 to the conductors 6| and 62,

' respectively. The terminals of the primary winding of the transformer 68 are connected to alternating current supply conductors L and L which may form a part of any availablealternating current supply system of customary commercial voltage for lighting and power purposes.

As diagrammatically shown, the shaft 66 is the armature shaft of a reversing motor including a rotor 1i and cooperating winding 12, and a second rotor 13 and cooperating winding 18, the shaft 66 being rotated in one direction when the winding 12 is energized, and in the opposite direction when the winding 18 is energized, as hereinafter described. One terminal of the winding 12 is connected through a limit switch 16 and a conductor 16 to the bridge conductor 62, to which one terminal of the winding 18 is also connected through the conductor 16 and a limit switch 11.

The second terminal of the winding 12 is connected to a switch contact 18, and the second terminal of the winding 14 is connected to a switch contact 18. A pivoted switch member 86, connected by a conductor 81 to the bridge conductor 61, is movable between one end position in which it engages the contact 16, and thereby connects the winding 12 between the bridge conthe armature 82 is given longitudinal reciprocating movements. It is given such movements by changes in the relative values of the currents flowing in the coils 83 and 84, which are arranged end to end and in inductive relation with the armature 82. The coils 83 and 84 are connected in series with one another between the conductors 6| and 62, and their adjacent terminals are connected by a conductor 86 to the bridge conductor 63.

, In any condition of stable operation, the currents flowing through the relay coils 83 and 84 will be equal, and the armature 82 and the switch will each be in its neutral position. Any deflection of the bell-crank 50 and contact 48 will make the currents flowing through the coils 83 and 84, unequal, and will result in an operation of the reversing motor which will adjust the contact 61 as required to rebalance those currents. For example, on a deflection of the contact 68 in the counter-clockwise direction, corresponding to a decrease in the temperature of the buib 8 below its normal value, the current flowing through the relay coil 84 will be increased relative to the current flow through the coil 83. In consequence, the armature 82 will be shifted to theright, bringing the pivoted switch 80 into engagement with the contact 19, and thereby energizing the motor winding 14. The rotor 13 will then rotate the shaft 68 in the counter-clockwise direction until the resultant movement of the contact 61 makes the sum of the portion of the resistance 65 between the contact 61 and conductor 62 and in the portion of the resistance 49 between the contact 48 and the conductor 6|, equal to the sum of the other portions of the resistances 49 and 65, whereupon the currents flowing through the relay coils 83 and 84 will be again equalized, and the armature 82 "will be returned to its mid position. Any adjustment of the contact 48 ineither direction, thus produces a corresponding proportional adjustment of the contact 6'! in one direction or the other.

The switches 15 and 11 are actuated by the rotation of the shaft 56 to perform the usual limit switch function of preventing overtravel of the armature shaft in either direction which would carry the contact 61 beyond the corresponding end of the resistance 65. As such motor limit switches are in common use, there is no occasion to illustrate or describe the connections through which the switches 15 and H are actuated by the shaft 56. As diagrammatically shown, the shaft 66 carries a worm 86 engaging the teeth of the worm gear segment 8! mounted on the operating shaft of the fuel valve 4 so that the latter is angularly adjusted in the opening or closing direction, as the bell-crank 50 deflects clockwise or counterclockwise, respectively, from its neutral position.

As shown, branch conductors 88 and 89 from the supply conductors L and L form the energizing conductors for the motor 46, and are included in a cable passing through the part 64. The latter is also formed with a passage for the tube 1 connecting the thermometer bulb to the helix 8.

While the essentialultimate elements of the apparatus have now been described, the control instrument includes practically necessary or desirable construction and adjustment features not previously mentioned. To vary the normal temperature of the bulb 8 which the apparatus tends to maintain, means are provided for adjusting the fulcrum pivot ii for the lever l5. As shown that pivot is carried by a bell crank lever 90 angularly adjustable about the pen axis l3, and adapted to be so adjusted by a link 8| connecting the lever 90 to a crank arm 92. The latter is carried by a rock shaft journaled in the instrument structure adjacent its periphery and adapted for angular adjustment by a screw driver engaging a kerf 93 in the front end of the shaft. The mounting of the shaft is such that it is frictionally held in any position into which it is adjusted. Angular adjustment of the lever 90 will not disturb the position of the pen arm I4, but will give a longitudinal adjustment to the link l8 and thereby effect an angular adjustment of the flapper valve operating lever is about its pivot 20, with the result of changing the angular position of the bell crank 50 assumed for any particular position of the pen arm l4. An indicating arm 94 may be secured to the lever 80 for the purpose of indicating on the record chart 41, the normal temperature which the apparatus is adjusted to maintain.

What instrument control range adjustment will give the best control results in furnace regulation or in the regulation of practically any industrial process or operation, will depend upon various factors, as those skilled in the control art will understand, and in particular, will depend upon the extent and rapidity of load changes tending to changes in the quantity measured, and on the rate of response to control changes. For example, in one installation, the total normal variation in furnace load or heat requirement, may be between a minimum and a maximum 50% larger than the minimum, while in another installation, the normal and to be expected maximum heat requirement may be several hundred per cent of the minimum heat requirement. A given change in the rate of fuel supply may produce a significant effect on the controlling temperature in five minutes in one installation, and in twenty minutes in another installation.

As a result of such variations in operating conditions, proper regulation, and the avoidance of an objectionable hunting tendency, may require that on a given change of load, the controlling temperature should be permitted to depart much more widely from the desired normal temperature in one installation than in another installation.

In general, the control range or adjustment of the bell-crank 50 and contact 48 may advantageously be greater for a given variation from. normal of the controlling temperature, when conditions permit variations in that temperature to be kept relatively small, than when conditions require that the maximum permitted controlling temperature variation should be relatively large. The wide variation in control range effected by adjustment of the member M in the instrument shown in Fig. 1, permits the instrument to be adjusted or calibrated to have the control range giving the best regulating results in installations having very different control requirements. For most uses of such apparatus as is shown in Fig. 1, there will be a crank 50 will be in or near its mid position. To

that end, the contact 61 and the spindle of the control valve 4 may well be relatively adjustable, as by angular adjustment of the contact 61 relative to the reversing motor shaft 68, so that when the contact 61 is in its mid position, the flow capacity of the fuel valve 4 will be that required to supply heat at the normal furnace load rate. In general, changes in operating conditions making desirable any significant change in the adjustment of the part 2|, will also make desirable adjustment of the contact 61 relative to the shaft 66.

In order to reverse the direction of operation of the valve 4 for a given change in-temperature it is only necessary to attach link l8 to the right end of lever l9 instead of to the left end as shown. This may be desirable in some cases for a particular condition or type of valve used.

In any instrument comprising a pneumatic power device or relay mechanism for adjusting some instrument device or mechanism in accordance with the movements of a sensitive movable measuring element, there are certain general advantages in placing a compressor, supplying air under pressure for the actuation of the power device or relay mechanism, in the inand means for returning said lever to its initialposition upon expansion of said balancing bellows.

9. In a control instrument, a member, means responsive to variations in a condition for deflecting said member, proportioning control means comprising in part an electrical resistance and a contact moving thereover, a pulsating pneumatic relay, connecting means between said relay and member for moving said contact in accordance with movements of said member, driving means for said relay comprising a pair of oppositely disposed bellows and means for alternately contracting and expanding said bellows to supply driving fluid to said relay.

10. In a control instrument, a member movable in response to variations in a controlled condition, a pair of alternately compressible bellows, means for compressing said bellows, proportioning means comprising an electrical resistance and a contact, a pair of regulating bellows connected respectively to said driving bellows, means controlled by, movement of said member in response to a variation of said condition to cause expansion of one of said regulating bellows upon compression of its driving bellows, means to move said contact over said resistance, said moving means being actuated by said regulating bellows, and means to adjust said condition responsive to movement of said contact.

11. In a control instrument, the combination with an instrument casing, of instrument mechanism mounted within said casing and comprising a member adapted to deflect in accordance with changes in a quantity measured, an adjustable device, pneumatic relay means controlled by said member and adapted to adjust said device, a pair of alternately compressible bellows adapted to supply air under pressure to said relay means, and a motor for compressing said bellows.

12. In a control instrument, proportioning means comprising a resistance and a contact adapted to move thereover, a pivoted lever to which said contact is attached, rack teeth on said lever, a pair of opposed regulating bellows, a pawl adapted to engage said rack teeth attached to each bellows, a member movable in response to variations in a condition, means controlled by movements. 01' aid member to permit expansion of one or the other of said bellows whereby upon expansion of said bellows said pawl will engage said rackteeth to move said lever and adjust said contactv along the resistance, and means to control said condition by said adjustment.

13. In a control instrument, a compressible driving bellows, a bleed nozzle and a balancing bellows connected thereto, means for periodically compressing said driving bellows, a flapper valve for closing said nozzle, 2. member responsive to variations in a condition, means permitting said valve to close said nozzle upon movement of said member whereby upon subsequent contraction of said driving bellows said balancing bellows will be expanded and means operable by expansion of said balancing bellows to return said valve to its initial position.

14. In an instrument, an element to be positioned, alternately acting opposed air motors adapted to position said element, a pulsating source of fluid under pressure connectedto said air motors, bleed valve means affecting communication of the pressure of said source to said air motors and means adapted to control said bleed valve means in accordance with the fluctuations of a variable condition.

15. In a control instrument a pair of cooperating control elements, a member deflecting in accordance with variations in a variable'condition, means for-relatively adjusting said control elements including a pair of alternately acting opposed air motors to perform such adjustment, a pulsating source of fluid under pressure, a pair of valves communicating with said source and said motors, means controlled by said member and adapted to control the relative positions of said valves and thereby vary the relative eifect of said motors upon said elements and means responsive to adjustment of said elements for effecting a readjustment of said valves.

16. The combination of claim 15 and means for varying the readjustment of said valve in response to a given air motor action.

17. In a control instrument, a member responsive to variations in a condition, means controlling said condition in response to movements of said member, said means including a proportioning system comprising a movable part, a pulsating pneumatic relay controlled by said member for moving said part, driving means for said relay, a pair of oppositely disposed bellows and means for alternately compressing and expanding said bellows to supply driving fluid for'said driving means.

EDWIN C. W'IEGMANN. 

